Iran's Chabahar Port Compared with Pakistan's Gwadar Port
By Riaz Haq
CA

Chabahar port in Iran is only about 100 miles from Gwadar port in Pakistan. Both are natural deep seaports in the Arabian sea.
Gwadar port's planned capacity is 300 to 400 million tons of cargo annually.  It is comparable to the capacity of all of India's ports combined - 500 million tons of cargo.   It is far larger than the 10-12 million tons cargo handling capacity planned for Chabahar. 

To put Gwadar's scale in perspective, let's compare it with the largest US port of Long Beach which handles 80 million tons of cargo, about a quarter of what Gwadar will handle upon completion of the project. Gawadar port will be capable of handling the world's largest container ships and massive oil tankers.
The port is being built in Pakistan by the Chinese as part of the ambitious $46 billion  China-Pakistan Economic Corridor (CPEC)  that will eventually serve as  Hong Kong West  for  growing Chinese trade with the Middle East and Europe.  CPEC will also enable Pakistan to bypass Afghanistan to trade with Central Asia through China across China's borders with Tajikistan, Kyrgyzstan and Kazakhstan. 
Chabahar is ostensibly an Indian effort to build a port in Iran to bypass Pakistan for India's trade with landlocked Afghanistan and other Central Asian states.  Prime Minister Modi has committed $500 million investment in Chabahar, a tiny fraction of the Chinese commitment for Gwadar. A trilateral agreement was recently signed in Tehran by Indian Prime Minister Modi, Iranian President Rouhani and Afghan President Ghani.
Trade with Afghanistan through Afghan-Iran border in the west will probably remain a pipe dream given that 1) most of the Afghan population lives in east and south close to the border with Pakistan and 2) Afghanistan has very poor infrastructure making it very difficult to move cargo across land from west to east and south of the country.
Pakistan suspects that India's real objective in Iran is to locate its intelligence agents under the cover of Chabahar port construction workers to sabotage the China-Pakistan Economic Corridor (CPEC) and support Baloch insurgency to  destabilize Pakistan . These suspicions were strengthened when Indian spy Kulbhushan Yadav, operating under the fake name of Husain Mubarak Patel, was arrested in Balochistan in March this year. Yadav confessed he was operating as an undercover RAW agent from his base in Chabahar, Iran.
If Iran does nothing to stop Indian overt activities from its soil against Pakistan, Iran-Pakistan relations could suffer irreparable harm. Efforts to sabotage CPEC will not please China either, and the Chinese are far more important to Iran as trading partners than India. This should give pause to hardline anti-Pakistan sectarian elements in Tehran.